This invention relates in general to a method of and apparatus for disposal of liquid waste material having contaminants dissolved or suspended therein and, in particular, to an evaporator system for disposing of contaminant bearing liquid by separating the liquid from the solid or suspended contaminants and discharging the solids material as a dry waste discharge.
More specifically, this invention relates to an evaporating method and apparatus whereby unclarified contaminant bearing liquid is passed into the evaporator system and sequentially exposed to heat through a system of conveying augers. The contaminated liquid is exposed to a heated surface and applied thereto by the augers to evaporate the liquid from the slurry thereby increasing the solids content of the slurry until such time as the liquid is removed or separated from the solids, at which time the solids are discharged from the evaporator system as a dry waste material.
Evaporator or still systems for disposal of liquid waste materials are generally used for low-volume liquid sludge concentrations which cannot be disposed of economically through any treatment by filtration, separation or chemical methods. While evaporation or distillation has been found to be the only economical method for disposal of certain types of contaminant bearing liquids, the existing systems have been found to be inefficient and unsatisfactory. In certain types of applications, such as contaminated water, the liquid portion of the contaminated liquid is usually boiled away until the solids concentration reaches a suitable percentage such that it may be manually removed from the still or distillation vat. In other types of situations, such as contaminated oil and water mixtures, the water is usually boiled off from the mixture leaving the oil bearing the contaminants. To dispose of the oil and contaminant slurry requires costly, inefficient and time consuming operations of the distillation apparatus.
Evaporation or distillation systems utilized in the treatment of contaminated liquids dispose of these materials by heating the liquid slurry until the liquid has reached its boiling point whereby the liquid is transformed into a vapor. The vapor can be vented into the atmosphere or passed through a condensing chamber for condensation if the liquid is to be recovered. The systems disclosed in the prior art are very inefficient due, in part, to the accumulation of the contaminants or solids material on the heating surfaces as the liquid material is evaporated from the slurry. This gradual buildup of the solids material on the heating surface prevents maximum heat transfer resulting in inefficient distillation, slow reclamation of the liquid and disposal of the solids.
Upon initial start up, the still apparatus efficiently transfers heat to the contaminated slurry. As the solids content is increased through the evaporation of distillation of the liquid, the resulting buildup of the solids material on the heating surface retards heat transfer to the slurry slowing the process and increasing its inefficiency. Certain types of existing distillation apparatus are placed under a vacuum to lower the pressure in the distillation chamber thereby decreasing the boiling or evaporation point and requiring less heat energy to effect evaporation. However, whether the distillation or evaporator apparatus is of the type wherein the distillation chamber is placed under a vacuum or is under atmospheric pressure, the device is still subjected to the problem of the solids buildup on the heating surface which retards the heat transfer and increases the system's inefficiency.
A further problem associated with known systems occurs since the distillation chambers of these devices are of a fixed volume. The slurry or liquid-solids contaminants which are placed within the distillation chamber are quiescent except for the agitation created when the liquid slurry is brought to its boiling point creating turbulence of the liquid and contaminants. However, as the liquid-solid slurry is agitated increasing the vaporization rate of the liquid from the slurry, the solids material begins building up on the heating surfaces forming an insulation barrier thereby decreasing the efficiency of the system and necessitating frequent cleaning of the distillation apparatus and sludge removal. In these devices the entire system must be shut down for the cleaning and removal of sludge from the distillation chamber. Therefore, none of these existing systems are sufficient to provide an efficient, economical method or apparatus for disposal of the low-volume liquid sludge slurries.